What is White noise?
White noise sources consist of thermal (Johnson or Nyquist) noise and shot noise. Thermal noise is generated by resistive elements and is linked to the random motion of carriers in electronic components, being solely dependent on temperature. On the other hand, shot noise is related to the discretization of charged particles and is consistently present in semiconductor pn junctions, being solely dependent on direct current (dc) flow.
The thermal noise of resistance, R, can be represented as an ideal resistor and an independent current or voltage source, illustrated in Figure 1.